Natural products from food sources can alter the spread of antimicrobial resistance plasmids in Enterobacterales

Antimicrobial resistance (AMR) poses a significant threat to global public health. Notably, resistance to carbapenem and extended-spectrum β-lactam antibiotics in Gram-negative bacteria is a major impediment to treating infections. Genes responsible for antibiotic resistance are frequently carried on plasmids, which can transfer between bacteria. Therefore, exploring strategies to prevent this transfer and the prevalence of AMR plasmids is timely and pertinent. Here, we show that certain natural product extracts and associated pure compounds can reduce the conjugation of AMR plasmids into new bacterial hosts. Using our established high-throughput fluorescence-based flow cytometry assay, we found that the natural products were more active in reducing transmission of the IncK extended-spectrum β-lactamase-encoding plasmid pCT in Escherichia coli EC958c, compared to Klebsiella pneumoniae Ecl8 carrying the IncFII carbapenemase-encoding plasmid pKpQIL. The exception was the natural product rottlerin, also active in K. pneumoniae. In classical conjugation assays, rottlerin also reduced the conjugation frequency of the IncFII bla NDM-1 carrying plasmid pCPE16_3 from a clinical K. pneumoniae isolate. Our data indicate that the natural products tested here, in their current molecular structure, reduced conjugation by a small amount, which is unlikely to achieve a large-scale reduction in AMR in bacterial populations. However, certain natural products like rottlerin could provide a foundation for further research into compounds with effective anti-plasmid activity.

Tracking intra-species and inter-genus transmission of KPC through global plasmids mining

Klebsiella pneumoniae carbapenemase (KPC) poses a major public health risk. Understanding its transmission dynamics requires examining the epidemiological features of related plasmids. Our study compiled 15,660 blaKPC-positive isolates globally over the past two decades. We found extensive diversity in the genetic background of KPC, with 23 Tn4401-related and 341 non-Tn4401 variants across 163 plasmid types in 14 genera. Intra-K. pneumoniae and cross-genus KPC transmission patterns varied across four distinct periods. In the initial periods, plasmids with narrow host ranges gradually established a survival advantage. In later periods, broad-host-range plasmids became crucial for cross-genera transmission. In total, 61 intra-K. pneumoniae and 66 cross-genus transmission units have been detected. Furthermore, phylogenetic reconstruction dated the origin of KPC transmission back to 1991 and revealed frequent exchanges across countries. Our research highlights the frequent and transient spread events of KPC mediated by plasmids across multiple genera and offers theoretical support for high-risk plasmid monitoring.

Cobalt complexes modulate plasmid conjugation in Escherichia coli and Klebsiella pneumoniae

Antimicrobial resistance genes (ARG), such as extended-spectrum β-lactamase (ESBL) and carbapenemase genes, are commonly carried on plasmids. Plasmids can transmit between bacteria, disseminate globally, and cause clinically important resistance. Therefore, targeting plasmids could reduce ARG prevalence, and restore the efficacy of existing antibiotics. Cobalt complexes possess diverse biological activities, including antimicrobial and anticancer properties. However, their effect on plasmid conjugation has not been explored yet. Here, we assessed the effect of four previously characterised bis(N-picolinamido)cobalt(II) complexes lacking antibacterial activity on plasmid conjugation in Escherichia coli and Klebsiella pneumoniae. Antimicrobial susceptibility testing of these cobalt complexes confirmed the lack of antibacterial activity in E. coli and K. pneumoniae. Liquid broth and solid agar conjugation assays were used to screen the activity of the complexes on four archetypical plasmids in E. coli J53. The cobalt complexes significantly reduced the conjugation of RP4, R6K, and R388 plasmids, but not pKM101, on solid agar in E. coli J53. Owing to their promising activity, the impact of cobalt complexes was tested on the conjugation of fluorescently tagged extended-spectrum β-lactamase encoding pCTgfp plasmid in E. coli and carbapenemase encoding pKpQILgfp plasmid in K. pneumoniae, using flow cytometry. The complexes significantly reduced the conjugation of pKpQILgfp in K. pneumoniae but had no impact on pCTgfp conjugation in E. coli. The cobalt complexes did not have plasmid-curing activity, suggesting that they target conjugation rather than plasmid stability. To our knowledge, this is the first study to report reduced conjugation of clinically relevant plasmids with cobalt complexes. These cobalt complexes are not cytotoxic towards mammalian cells and are not antibacterial, therefore they could be optimised and employed as inhibitors of plasmid conjugation.

Carbapenem-resistant Klebsiella pneumoniae: the role of plasmids in emergence, dissemination, and evolution of a major clinical challenge

INTRODUCTION

Klebsiella pneumoniae is a major agent of healthcare-associated infections and a cause of some community-acquired infections, including severe bacteremic infections associated with metastatic abscesses in liver and other organs. Clinical relevance is compounded by its outstanding propensity to evolve antibiotic resistance. In particular, the emergence and dissemination of carbapenem resistance in K. pneumoniae has posed a major challenge due to the few residual treatment options, which have only recently been expanded by some new agents. The epidemiological success of carbapenem-resistant K. pneumoniae (CR-Kp) is mainly linked with clonal lineages that produce carbapenem-hydrolyzing enzymes (carbapenemases) encoded by plasmids.

AREAS COVERED

Here, we provide an updated overview on the mechanisms underlying the emergence and dissemination of CR-Kp, focusing on the role that plasmids have played in this phenomenon and in the co-evolution of resistance and virulence in K. pneumoniae.

EXPERT OPINION

CR-Kp have disseminated on a global scale, representing one of the most important contemporary public health issues. These strains are almost invariably associated with complex multi-drug resistance (MDR) phenotypes, which can also include recently approved antibiotics. The heterogeneity of the molecular bases responsible for these phenotypes poses significant hurdles for therapeutic and diagnostic purposes.

Isolation and Characterisation of Human-Derived blaKPC-3-Producing Salmonella enterica Serovar Rissen in 2018

In this study, we describe a Salmonella enterica serovar (S.) Rissen strain with a reduced susceptibility to meropenem, isolated from a urinary infection in an 89-year-old woman in 2018 during activity surveillance in Italy (Enter-Net Italia). The genomic characteristics, pathogenicity, and antimicrobial resistance mechanisms were investigated via a genomic approach. Antimicrobial susceptibility testing revealed a "susceptible, increased exposure" phenotype to meropenem in the S. Rissen strain (4_29_19). Whole-genome sequencing (WGS) was performed using both the NovaSeq 6000 S4 PE150 XP platform (Illumina, San Diego, CA, USA) and MinION (Oxford Nanopore). The S. Rissen 4_29_19 strain harboured two plasmids: a pKpQIL-like plasmid carrying the blaKPC-3 resistance gene in a Tn4401a transposon (pKPC_4_29_19), and a ColE-like plasmid (p4_4_29_19) without resistance genes, highly prevalent among Enterobacterales. Comparative analysis revealed that the pKPC_4_29_19 plasmid was highly related to the pKpQIL reference plasmid (GU595196), with 57% coverage and 99.96% identity, but lacking a region of about 30 kb, involving the FIIK2 replicon region and the entire transfer locus, causing the loss of its ability to conjugate. To our knowledge, this is the first time that a pKpQIL-like plasmid, carrying blaKPC-3, highly diffused in Klebsiella pneumoniae strains, has been identified in a Salmonella strain in our country. The acquisition of blaKPC genes by Salmonella spp. is extremely rare, and is reported only sporadically. In zoonotic bacteria isolated from humans, the presence of a carbapenem resistance gene carried by mobile genetic elements, usually described in healthcare-associated infection bacteria, represents an important concern for public health.

Genomic Characteristics and Molecular Epidemiology of Multidrug-Resistant Klebsiella pneumoniae Strains Carried by Wild Birds

This study aimed to explore the relationship between wild birds and the transmission of multidrug-resistant strains. Klebsiella pneumoniae was isolated from fresh feces of captured wild birds and assessed by the broth microdilution method and comparative genomics. Four Klebsiella pneumoniae isolates showed different resistance phenotypes; S90-2 and S141 were both resistant to ampicillin, cefuroxime, and cefazolin, while M911-1 and S130-1 were sensitive to most of the 14 antibiotics tested. S90-2 belongs to sequence type 629 (ST629), and its genome includes 30 resistance genes, including blaCTX-M-14 and blaSHV-11, while its plasmid pS90-2.3 (IncR) carries qacEdelta1, sul1, and aph(3')-Ib. S141 belongs to ST1662, and its genome includes a total of 27 resistance genes, including blaSHV-217. M911-1 is a new ST, carrying blaSHV-1 and fosA6, and its plasmid pM911-1.1 (novel) carries qnrS1, blaLAP-2, and tet(A). S130-1 belongs to ST3753, carrying blaSHV-11 and fosA6, and its plasmid pS130-1 [IncFIB(K)] carries only one resistance gene, tet(A). pM911-1.1 and pS90-2.3 do not have conjugative transfer ability, but their resistance gene fragments are derived from multiple homologous Enterobacteriaceae strain chromosomes or plasmids, and the formation of resistance gene fragments (multidrug resistance region) involves interactions between multiple mobile element genes, resulting in a complex and diverse resistance plasmid structure. The homologous plasmids related to pM911-1.1 and pS90-2.3 were mainly from isolated human-infecting bacteria in China, namely, K. pneumoniae and Escherichia coli. The multidrug-resistant K. pneumoniae isolates carried by wild birds in this study had drug resistance phenotypes conferred primarily by multidrug resistance plasmids that were closely related to human-infecting bacteria. IMPORTANCE Little is known about the pathogenic microorganisms carried by wild animals. This study found that the multidrug resistance phenotype of Klebsiella pneumoniae isolates carried by wild birds was mainly attributed to multidrug resistance plasmids, and these multidrug resistance plasmids from wild birds were closely related to human-infecting bacteria. Wild bird habitats overlap to a great extent with human and livestock habitats, which further increases the potential for horizontal transfer of multidrug-resistant bacteria among humans, animals, and the environment. Therefore, wild birds, as potential transmission hosts of multidrug-resistant bacteria, should be given attention and monitored.

Mating pair stabilization mediates bacterial conjugation species specificity

Bacterial conjugation mediates contact-dependent transfer of DNA from donor to recipient bacteria, thus facilitating the spread of virulence and resistance plasmids. Here we describe how variants of the plasmid-encoded donor outer membrane (OM) protein TraN cooperate with distinct OM receptors in recipients to mediate mating pair stabilization and efficient DNA transfer. We show that TraN from the plasmid pKpQIL (Klebsiella pneumoniae) interacts with OmpK36, plasmids from R100-1 (Shigella flexneri) and pSLT (Salmonella Typhimurium) interact with OmpW, and the prototypical F plasmid (Escherichia coli) interacts with OmpA. Cryo-EM analysis revealed that TraN_pKpQIL interacts with OmpK36 through the insertion of a β-hairpin in the tip of TraN into a monomer of the OmpK36 porin trimer. Combining bioinformatic analysis with AlphaFold structural predictions, we identified a fourth TraN structural variant that mediates mating pair stabilization by binding OmpF. Accordingly, we devised a classification scheme for TraN homologues on the basis of structural similarity and their associated receptors: TraNα (OmpW), TraNβ (OmpK36), TraNγ (OmpA), TraNδ (OmpF). These TraN-OM receptor pairings have real-world implications as they reflect the distribution of resistance plasmids within clinical Enterobacteriaceae isolates, demonstrating the importance of mating pair stabilization in mediating conjugation species specificity. These findings will allow us to predict the distribution of emerging resistance plasmids in high-risk bacterial pathogens.

Combining conjugation and structural analyses, the authors show that TraN-OMP pairings determine bacterial conjugation species specificity, with implications in resistance plasmid distribution within Enterobacteriaceae.

Population structure of blaKPC-harbouring IncN plasmids at a New York City medical centre and evidence for multi-species horizontal transmission

BACKGROUND

Carbapenem-resistant Enterobacterales (CRE) are highly concerning MDR pathogens. Horizontal transfer of broad-host-range IncN plasmids may contribute to the dissemination of the Klebsiella pneumoniae carbapenemase (KPC), spreading carbapenem resistance among unrelated bacteria. However, the population structure and genetic diversity of IncN plasmids has not been fully elucidated.

OBJECTIVES

We reconstructed blaKPC-harbouring IncN plasmid genomes to characterize shared gene content, structural variability, and putative horizontal transfer within and across patients and diverse bacterial clones.

METHODS

We performed short- and long-read sequencing and hybrid assembly on 45 CRE isolates with blaKPC-harbouring IncN plasmids. Eight serial isolates from two patients were included to assess intra-patient plasmid dynamics. Comparative genomic analysis was performed to assess structural and sequence similarity across plasmids. Within IncN sublineages defined by plasmid MLST and kmer-based clustering, phylogenetic analysis was used to identify closely related plasmids.

RESULTS

Comparative analysis of IncN plasmid genomes revealed substantial heterogeneity including large rearrangements in serial patient plasmids and differences in structure and content across plasmid clusters. Within plasmid sublineages, core genome content and resistance gene regions were largely conserved. Closely related plasmids (≤1 SNP) were found in highly diverse isolates, including ten pST6 plasmids found in eight bacterial clones from three different species.

CONCLUSIONS

Genomic analysis of blaKPC-harbouring IncN plasmids revealed the presence of several distinct sublineages as well as substantial host diversity within plasmid clusters suggestive of frequent mobilization. This study reveals complex plasmid dynamics within a single plasmid family, highlighting the challenge of tracking plasmid-mediated transmission of blaKPC in clinical settings.

Diversity of carbapenemase-producing Enterobacterales in England as revealed by whole-genome sequencing of isolates referred to a national reference laboratory over a 30-month period

Introduction. Increasing numbers of carbapenemase-producing Enterobacterales (CPE), which can be challenging to treat, have been referred to the national reference laboratory in England since the early 2000s.Gap Statement/Aim. Previous studies on CPE in the UK have focussed on localized outbreaks. We applied whole-genome sequencing (WGS) to isolates referred to the national reference laboratory over 30 months to inform our understanding of CPE epidemiology in England.Methodology. The first confirmed CPE from each new patient referred by an English diagnostic laboratory between 1 January 2014 and 30 June 2016 was sequenced on an Illumina HiSeq 2500. Multiple isolates from the same patient were included from either different species or the same species with different carbapenemase genes. The data were analysed using an in-house bioinformatics pipeline that determines species identification, multi-locus sequence typing (MLST) profile and antimicrobial resistance gene content.Results. A total of 2658 non-duplicate CPE were sequenced amongst which three host organisms belonging to diverse sequence types (STs) predominated: Klebsiella pneumoniae (1380/2658, 51.9 %; 177 STs), Escherichia coli (723/2658, 27.2 %; 133 STs) and Enterobacter cloacae (294/2658, 11.1 %; 88 STs). Thirty different carbapenemase gene variants were identified, although bla _OXA-48-like (1122/2658, 42.2%), bla _NDM (692/2658, 26.0 %), bla _KPC (571/2658, 21.5 %), bla _VIM (100/2658, 3.8 %) and bla _IMP (33/2658, 1.2 %) predominated. ST/carbapenemase gene pairings represented widely distributed high-risk clones or clusters at a regional or hospital level.Conclusion. CPE referred to the national reference laboratory are diverse, suggesting multiple introductions to England and a role for horizontal transfer of carbapenemase genes in English CPE epidemiology.

Accessory Genomes Drive Independent Spread of Carbapenem-Resistant Klebsiella pneumoniae Clonal Groups 258 and 307 in Houston, TX

Carbapenem-resistant Klebsiella pneumoniae (CRKp) is an urgent public health threat. Worldwide dissemination of CRKp has been largely attributed to clonal group (CG) 258. However, recent evidence indicates the global emergence of a CRKp CG307 lineage. Houston, TX, is the first large city in the United States with detected cocirculation of both CRKp CG307 and CG258. We sought to characterize the genomic and clinical factors contributing to the parallel endemic spread of CG258 and CG307. CRKp isolates were collected as part of the prospective, Consortium on Resistance against Carbapenems in Klebsiella and other Enterobacterales 2 (CRACKLE-2) study. Hybrid short-read and long-read genome assemblies were generated from 119 CRKp isolates (95 originated from Houston hospitals). A comprehensive characterization of phylogenies, gene transfer, and plasmid content with pan-genome analysis was performed on all CRKp isolates. Plasmid mating experiments were performed with CG307 and CG258 isolates of interest. Dissection of the accessory genomes suggested independent evolution and limited horizontal gene transfer between CG307 and CG258 lineages. CG307 contained a diverse repertoire of mobile genetic elements, which were shared with other non-CG258 K. pneumoniae isolates. Three unique clades of Houston CG307 isolates clustered distinctly from other global CG307 isolates, indicating potential selective adaptation of particular CG307 lineages to their respective geographical niches. CG307 strains were often isolated from the urine of hospitalized patients, likely serving as important reservoirs for genes encoding carbapenemases and extended-spectrum β-lactamases. Our findings suggest parallel cocirculation of high-risk lineages with potentially divergent evolution. IMPORTANCE The prevalence of carbapenem-resistant Klebsiella pneumoniae (CRKp) infections in nosocomial settings remains a public health challenge. High-risk clones such as clonal group 258 (CG258) are particularly concerning due to their association with blaKPC carriage, which can severely complicate antimicrobial treatments. There is a recent emergence of clonal group 307 (CG307) worldwide with little understanding of how this successful clone has been able to adapt while cocirculating with CG258. We provide the first evidence of potentially divergent evolution between CG258 and CG307 with limited sharing of adaptive genes. Houston, TX, is home to the largest medical center in the world, with a large influx of domestic and international patients. Thus, our unique geographical setting, where two pandemic strains of CRKp are circulating, provides an indication of how differential accessory genome content can drive stable, endemic populations of CRKp. Pan-genomic analyses such as these can reveal unique signatures of successful CRKp dissemination, such as the CG307-associated plasmid (pCG307_HTX), and provide invaluable insights into the surveillance of local carbapenem-resistant Enterobacterales (CRE) epidemiology.

Evolutionary Trajectories toward Ceftazidime-Avibactam Resistance in Klebsiella pneumoniae Clinical Isolates

From January 2019 to April 2020, 32 KPC-producing, ceftazidime-avibactam (CZA) resistant Klebsiella pneumoniae strains were isolated in a university hospital in Rome, Italy. These strains belonged to the ST512, ST101 and ST307 high-risk clones. Nine different CZA-resistant KPC-3 protein variants were identified, five of them never previously reported (KPC-66 to KPC-70). Among them, KPC-31, KPC-39, KPC-49, KPC-66, KP-68, KPC-69 and KPC-70 showed amino acid substitutions, insertions and deletions in the Ω loop of the protein. KPC-29 has the duplication, while the novel KPC-67 has the triplication of the KDD triplet in the 270-loop of the protein. Genomics performed on contemporary resistant and susceptible clones underlined that those novel mutations emerged in bla_KPC-3 genes located on conserved plasmids: in ST512, all bla_KPC-3 mutant genes were located in pKpQIL plasmids, while the three novel bla_KPC-3 mutants identified in ST101 were on FIIk-FIA(HI1)-R plasmids. Selection also promoted multiplication of the carbapenemase gene copy number by transposition, recombination, and fusion of resident plasmids. When expressed in Escherichia coli recipient cells cloned in the high-copy number pTOPO vector, the Ω loop mutated variants showed CZA-resistant phenotype associated with susceptibility to carbapenems, while KPC variants with insertions in the 270-loop showed residual activity on carbapenems. The investigation of CZA-resistance mechanisms offered the unique opportunity to study vertical, horizontal, and oblique evolutionary trajectories of K. pneumoniae high-risk clones.

Concomitant carriage of KPC-producing and non-KPC-producing Klebsiella pneumoniae ST512 within a single patient

BACKGROUND

KPC-producing Klebsiella pneumoniae of clonal group 258 are prominent in healthcare settings in many regions of the world. The blaKPC gene is mostly carried by a multireplicon IncFIIk-IncFI plasmid suspected to be highly compatible and stable in this genetic background. Here, we analysed the genetic diversity of an ST512 K. pneumoniae population in a single patient.

METHODS

Twelve K. pneumoniae isolates (n = 5 from urine samples and n = 7 from rectal swabs) were recovered from one patient over a 2 month period. Antimicrobial susceptibility testing, plasmid extraction and WGS were performed on all isolates. The first K. pneumoniae isolate, D1, was used as a reference for phylogenetic analysis.

RESULTS

Antimicrobial susceptibility testing, plasmid analysis and WGS revealed concomitant carriage of carbapenem-resistant and carbapenem-susceptible K. pneumoniae isolates of ST512, with the absence of the entire blaKPC-carrying plasmid in the susceptible population. Furthermore, 14 other genetic events occurred within the genome, including 3 chromosomal deletions (of 71 kb, 33 kb and 11 bp), 2 different insertions of ISKpn26 and 9 SNPs. Interestingly, most of the events occurred in the same chromosomal region that has been deleted independently several times, probably after homologous recombination involving 259 bp repeated sequences.

CONCLUSIONS

Our study revealed (to the best of our knowledge) the first case of in vivo blaKPC-carrying plasmid curing and a wide within-patient genetic diversity of a single K. pneumoniae ST512 clone over a short period of carriage. This within-patient diversity must be taken into account when characterizing transmission chains using WGS during nosocomial outbreaks.

Distinguishing bla KPC Gene-Containing IncF Plasmids from Epidemiologically Related and Unrelated Enterobacteriaceae Based on Short- and Long-Read Sequence Data

Limited information is available on whether bla _KPC-containing plasmids from isolates in a hospital outbreak can be differentiated from epidemiologically unrelated bla _KPC-containing plasmids based on sequence data. This study aimed to evaluate the performance of three approaches to distinguish epidemiologically related from unrelated bla _KPC-containing pKpQiL-like IncFII(k2)-IncFIB(pQiL) plasmids. Epidemiologically related isolates were subjected to short- and long-read whole-genome sequencing. A hybrid assembly was performed, and plasmid sequences were extracted from the assembly graph. Epidemiologically unrelated plasmid sequences were extracted from GenBank. Pairwise comparisons of epidemiologically related and unrelated plasmids based on SNPs using snippy and of phylogenetic distance using Roary and using a similarity index that penalizes size differences between plasmids (Stoesser index) were performed. The percentage of pairwise comparisons misclassified as genetically related or as clonally unrelated was determined using different genetic thresholds for genetic relatedness. The ranges of number of SNPs, Roary phylogenetic distance, and Stoesser index overlapped between the epidemiologically related and unrelated plasmids. When a genetic similarity threshold that classified 100% of epidemiologically related plasmid pairs as genetically related was used, the percentages of plasmids misclassified as epidemiologically related ranged from 6.7% (Roary) to 20.8% (Stoesser index). Although epidemiologically related plasmids can be distinguished from unrelated plasmids based on genetic differences, bla _KPC-containing pKpQiL-like IncFII(k2)-IncFIB(pQiL) plasmids show a high degree of sequence similarity. The phylogenetic distance as determined using Roary showed the highest degree of discriminatory power between the epidemiologically related and unrelated plasmids.

Prevalence of blaKPC-2, blaKPC-3 and blaKPC-30-Carrying Plasmids in Klebsiella pneumoniae Isolated in a Brazilian Hospital

Klebsiella pneumoniae carbapenemase (KPC) actively hydrolyzes carbapenems, antibiotics often used a last-line treatment for multidrug-resistant bacteria. KPC clinical relevance resides in its widespread dissemination. In this work, we report the genomic context of KPC coding genes bla_KPC-2, bla_KPC-3 and bla_KPC-30 in multidrug-resistant Klebsiellapneumoniae isolates from Brazil. Plasmids harboring bla_KPC-3 and bla_KPC-30 were identified. Fifteen additional carbapenem-resistant K. pneumoniae isolates were selected from the same tertiary hospital, collected over a period of 8 years. Their genomes were sequenced in order to evaluate the prevalence and dissemination of bla_KPC-harboring plasmids. We found that bla_KPC genes were mostly carried by one of two isoforms of transposon Tn4401 (Tn4401a or Tn4401b) that were predominantly located on plasmids highly similar to the previously described plasmid pKPC_FCF3SP (IncN). The identified pKPC_FCF3SP-like plasmids carried either bla_KPC-2 or bla_KPC-30. Two K. pneumoniae isolates harbored pKpQIL-like (IncFII) plasmids, only recently identified in Brazil; one of them harbored bla_KPC-3 in a Tn4401a transposon. Underlining the risk of horizontal spread of KPC coding genes, this study reports the prevalence of bla_KPC-2 and the recent spread of bla_KPC-3, and bla_KPC-30, in association with different isoforms of Tn4401, together with high synteny of plasmid backbones among isolates studied here and in comparison with previous reports.

Cefepime/tazobactam compared with other tazobactam combinations against problem Gram-negative bacteria

OBJECTIVES

Piperacillin/tazobactam has long been a broad-spectrum 'workhorse' antibiotic; however, it is compromised by resistance. One response is to re-partner tazobactam with cefepime, which is easier to protect, being less β-lactamase labile, and to use a high-dose and prolonged infusion. On this basis, Wockhardt are developing cefepime/tazobactam (WCK 4282) as a 2+2 g q8h combination with a 90-min infusion.

METHODS

The activity of cc cefepime/tazobactam was assessed, with other tazobactam combinations as comparators, against 1632 Enterobacterales, 745 Pseudomonas aeruginosa and 450 other non-fermenters, as submitted to the UK National Reference Laboratory. These were categorised by carbapenemase-gene detection and interpretive reading of phenotypes, with MICs determined by British Society for Antimicrobial Chemotherapy agar dilution.

RESULTS

Although higher breakpoints may be justifiable, based on the pharmacodynamics, the results were reviewed against current cefepime criteria. On this basis, cefepime/tazobactam was broadly active against Enterobacterales with AmpC enzymes and extended-spectrum β-lactamases (ESBLs), even when they had ertapenem resistance, suggesting porin loss. At 8+8 mg/L, activity extended to > 90% of Enterobacterales with OXA-48 and KPC carbapenemases, although the MICs for KPC producers belonging to the international Klebsiella pneumoniae ST258 lineage were higher; metallo-β-lactamase producers remained resistant. Cefepime/tazobactam was less active than ceftolozane/tazobactam against Pseudomonas aeruginosa with AmpC de-repression or high-level efflux but achieved wider antipseudomonal coverage than piperacillin/tazobactam. Activity against other non-fermenters was species-specific.

CONCLUSION

Overall, cefepime/tazobactam had a spectrum exceeding those of piperacillin/tazobactam and ceftolozane/tazobactam and resembling or exceeding that of carbapenems. Used as a 'new-combination of old-agents' it has genuine potential to be 'carbapenem-sparing'.

A high prevalence of blaOXA-48 in Klebsiella (Raoultella) ornithinolytica and related species in hospital wastewater in South West England

Klebsiella species occupy a wide range of environmental and animal niches, and occasionally cause opportunistic infections that are resistant to multiple antibiotics. In particular, Klebsiella pneumoniae (Kpne) has gained notoriety as a major nosocomial pathogen, due principally to the rise in non-susceptibility to carbapenems and other beta-lactam antibiotics. Whilst it has been proposed that the urban water cycle facilitates transmission of pathogens between clinical settings and the environment, the level of risk posed by resistant Klebsiella strains in hospital wastewater remains unclear. We used whole genome sequencing (WGS) to compare Klebsiella species in contemporaneous samples of wastewater from an English hospital and influent to the associated wastewater treatment plant (WWTP). As we aimed to characterize representative samples of Klebsiella communities, we did not actively select for antibiotic resistance (other than for ampicillin), nor for specific Klebsiella species. Two species, Kpne and K. (Raoultella) ornithinolytica (Korn), were of equal dominance in the hospital wastewater, and four other Klebsiella species were present in low abundance in this sample. In contrast, despite being the species most closely associated with healthcare settings, Kpne was the dominant species within the WWTP influent. In total, 29 % of all isolates harboured the blaOXA-48 gene on a pOXA-48-like plasmid, and these isolates were almost exclusively recovered from the hospital wastewater. This gene was far more common in Korn (68 % of isolates) than in Kpne (3.4 % of isolates). In general plasmid-borne, but not chromosomal, resistance genes were significantly enriched in the hospital wastewater sample. These data implicate hospital wastewater as an important reservoir for antibiotic-resistant Klebsiella, and point to an unsuspected role of species within the Raoultella group in the maintenance and dissemination of plasmid-borne blaOXA-48. This article contains data hosted by Microreact.

Characterization of blaKPC-2-Harboring Klebsiella pneumoniae Isolates and Mobile Genetic Elements from Outbreaks in a Hospital in Ecuador

Aim: To investigate the mobile genetic elements harboring bla_KPC gene in carbapenem-resistant Klebsiella pneumoniae recovered during a 6-month outbreak in a high-complexity hospital from Ecuador. Results: A total of 62 isolates belonging to ST258 pilv-I-positive (n = 45), ST25 serotype K2 (n = 8), ST348 (n = 6), ST42 (n = 1), ST196 (n = 1), and ST1758 (n = 1) were collected from intensive care unit (ICU), neurosurgery, burn unit, internal medicine, pneumology, and neurology. Pulsed-field gel electrophoresis analysis showed two major clusters of ST258 and ST25 related to bloodstream infections and pneumonia circulating in ICU. The PCR assay showed that in non-ST258 isolates, the bla_KPC-2 gene were located on the Tn4401a transposon inserted in the transferable pKpQIL-like IncFII_K2 plasmid; the whole-genome sequencing of ST258 clone showed two plasmids, the bla_KPC-2 gene was located on nonconjugative IncR plasmid, whereas the IncFIB/IncFII plasmid lacked ß-lactamase genes. We found an IncM plasmid in bla_KPC-2-harboring Klebsiella pneumoniae ST1758 clone. Conclusions: These findings highlight the presence of pKpQIL-like plasmids in non-ST258 and nonconjugative plasmids in ST258 isolates causing hospital outbreaks.

Integrated chromosomal and plasmid sequence analyses reveal diverse modes of carbapenemase gene spread among Klebsiella pneumoniae

Molecular and genomic surveillance systems for bacterial pathogens currently rely on tracking clonally evolving lineages. By contrast, plasmids are usually excluded or analyzed with low-resolution techniques, despite being the primary vectors of antibiotic resistance genes across many key pathogens. Here, we used a combination of long- and short-read sequence data of Klebsiella pneumoniae isolates (n = 1,717) from a European survey to perform an integrated, continent-wide study of chromosomal and plasmid diversity. This revealed three contrasting modes of dissemination used by carbapenemase genes, which confer resistance to last-line carbapenems. First, bla_OXA-48-like genes have spread primarily via the single epidemic pOXA-48-like plasmid, which emerged recently in clinical settings and spread rapidly to numerous lineages. Second, bla_VIM and bla_NDM genes have spread via transient associations of many diverse plasmids with numerous lineages. Third, bla_KPC genes have transmitted predominantly by stable association with one successful clonal lineage (ST258/512) yet have been mobilized among diverse plasmids within this lineage. We show that these plasmids, which include pKpQIL-like and IncX3 plasmids, have a long association (and are coevolving) with the lineage, although frequent recombination and rearrangement events between them have led to a complex array of mosaic plasmids carrying bla_KPC Taken altogether, these results reveal the diverse trajectories of antibiotic resistance genes in clinical settings, summarized as using one plasmid/multiple lineages, multiple plasmids/multiple lineages, and multiple plasmids/one lineage. Our study provides a framework for the much needed incorporation of plasmid data into genomic surveillance systems, an essential step toward a more comprehensive understanding of resistance spread.

Carbapenem Resistance-Encoding and Virulence-Encoding Conjugative Plasmids in Klebsiella pneumoniae

Klebsiella pneumoniae has an exceptional ability to acquire exogenous resistance-encoding and hypervirulence-encoding genetic elements. In this review we trace the key evolutionary routes of plasmids involved in the dissemination of such elements; we observed diverse, but convergent, evolutionary paths that eventually led to the emergence of conjugative plasmids which simultaneously encode carbapenem resistance and hypervirulence. One important evolutionary feature of these plasmids is that they contain a wide range of transposable elements that enable them to undergo frequent genetic transposition, resulting in plasmid fusion and presumably better adaptation of the plasmid to the bacterial host. Identifying the key molecular markers of resistance and virulence-bearing conjugative plasmids allows improved tracking and control of the life-threatening carbapenem-resistant and hypervirulent strains of K. pneumoniae.

Evaluation of the MBT STAR-Carba Assay for the Detection of Carbapenemase Production in Enterobacteriaceae and Hafniaceae with a Large Collection of Routine Isolates from Plate Cultures and Patient-Derived Positive Blood Cultures

The spread of carbapenemase-producing Enterobacterales is a major public health concern worldwide, and methods for their prompt and reliable detection are highly demanded for therapeutic and hygiene control purposes. In this study, we evaluate the MBT STAR^®-Carba assay (Bruker Daltonik) to detect the carbapenemase production in clinical and surveillance isolates from plate cultures and directly from patient-derived positive blood cultures bottles. Overall, n = 1,307 samples were analyzed (n = 900 plate cultures, and n = 407 positive blood cultures, using the bacterial pellet obtained with the Sepsityper^® Kit; Bruker Daltonik), including n = 793 carbapenemase producers (n = 579 Klebsiella pneumoniae carbapenemase, n = 161 metallo-beta-lactamases, n = 45 OXA-48, and eight isolates harboring two different enzymes), n = 239 carbapenem-resistant noncarbapenemase producers, and n = 275 carbapenem-susceptible strains. The STAR-Carba assay detected 657/661 (99.4%) carbapenemase producers from plate cultures, and 132/132 (100%) from positive blood cultures. Specificity resulted in 100% for carbapenem-susceptible strains, and 91.6% for carbapenem-resistant strains resulted negative for carbapenamase production with the routine methods used in this study. In this study, the MBT STAR-Carba assay proved to be a highly reliable method for the detection of carbapenemase-producing Enterobacterales, regardless of the enzyme family, and from both plate cultures and positive blood culture bottles.

Mobile genetic elements associated with carbapenemase genes in South American Enterobacterales

Introduction

Carbapenem resistance in members of order Enterobacterales is a growing public health problem causing high mortality in developing and industrialized countries. Its emergence and rapid propagation worldwide was due to both intercontinental spread of pandemic strains and horizontal dissemination via mobile genetic elements (MGE) such as plasmids and transposons.

Objective

To describe MGE carrying carbapenem resistance genes in Enterobacterales which have been reported in South America.

Search strategy and selection criteria

A search of the literature in English or Spanish published until 2019 in PubMed, Google Scholar, LILACS and SciELO databases was performed for studies of MGE in Enterobacterales reported in South American countries.

Results

Seven South American countries reported MGE related to carbapenemases. Carbapenemase-producing Klebsiella pneumoniae belonging to clonal complex 258 were the most prevalent pathogens reported; others carbapenemase-producing Enterobacterales such as Escherichia coli, Serratia marcescens, and Providencia rettgeri also have been reported. The MGE implicated in the spread of the most prevalent carbapenemase genes are Tn4401 and non-Tn4401 elements for bla_KPC and ISAba125 for bla_NDM, located in different plasmid incompatibility groups, i.e. L/M, A/C, FII and bacterial clones.

Conclusion

This review indicates that, like in other parts of the world, the most commonly reported carbapenemases in Enterobacterales from South America are being disseminated through clones, plasmids, and transposons which have been previously reported in other parts of the world.

Genomic Epidemiology of Complex, Multispecies, Plasmid-Borne bla KPC Carbapenemase in Enterobacterales in the United Kingdom from 2009 to 2014

Carbapenem resistance in Enterobacterales is a public health threat. Klebsiella pneumoniae carbapenemase (encoded by alleles of the bla _KPC family) is one of the most common transmissible carbapenem resistance mechanisms worldwide. The dissemination of bla _KPC historically has been associated with distinct K. pneumoniae lineages (clonal group 258 [CG258]), a particular plasmid family (pKpQIL), and a composite transposon (Tn4401). In the United Kingdom, bla _KPC has represented a large-scale, persistent management challenge for some hospitals, particularly in North West England. The dissemination of bla _KPC has evolved to be polyclonal and polyspecies, but the genetic mechanisms underpinning this evolution have not been elucidated in detail; this study used short-read whole-genome sequencing of 604 bla _KPC-positive isolates (Illumina) and long-read assembly (PacBio)/polishing (Illumina) of 21 isolates for characterization. We observed the dissemination of bla _KPC (predominantly bla _KPC-2; 573/604 [95%] isolates) across eight species and more than 100 known sequence types. Although there was some variation at the transposon level (mostly Tn4401a, 584/604 [97%] isolates; predominantly with ATTGA-ATTGA target site duplications, 465/604 [77%] isolates), bla _KPC spread appears to have been supported by highly fluid, modular exchange of larger genetic segments among plasmid populations dominated by IncFIB (580/604 isolates), IncFII (545/604 isolates), and IncR (252/604 isolates) replicons. The subset of reconstructed plasmid sequences (21 isolates, 77 plasmids) also highlighted modular exchange among non-bla _KPC and bla _KPC plasmids and the common presence of multiple replicons within bla _KPC plasmid structures (>60%). The substantial genomic plasticity observed has important implications for our understanding of the epidemiology of transmissible carbapenem resistance in Enterobacterales for the implementation of adequate surveillance approaches and for control.

HIV Drugs Inhibit Transfer of Plasmids Carrying Extended-Spectrum β-Lactamase and Carbapenemase Genes

Antimicrobial-resistant (AMR) infections pose a serious risk to human and animal health. A major factor contributing to this global crisis is the sharing of resistance genes between different bacteria via plasmids. The WHO lists Enterobacteriaceae, such as Escherichia coli and Klebsiella pneumoniae, producing extended-spectrum β-lactamases (ESBL) and carbapenemases as "critical" priorities for new drug development. These resistance genes are most often shared via plasmid transfer. However, finding methods to prevent resistance gene sharing has been hampered by the lack of screening systems for medium-/high-throughput approaches. Here, we have used an ESBL-producing plasmid, pCT, and a carbapenemase-producing plasmid, pKpQIL, in two different Gram-negative bacteria, E. coli and K. pneumoniae Using these critical resistance-pathogen combinations, we developed an assay using fluorescent proteins, flow cytometry, and confocal microscopy to assess plasmid transmission inhibition within bacterial populations in a medium-throughput manner. Three compounds with some reports of antiplasmid properties were tested; chlorpromazine reduced transmission of both plasmids and linoleic acid reduced transmission of pCT. We screened the Prestwick library of over 1,200 FDA-approved drugs/compounds. From this, we found two nucleoside analogue drugs used to treat HIV, abacavir and azidothymidine (AZT), which reduced plasmid transmission (AZT, e.g., at 0.25 μg/ml reduced pCT transmission in E. coli by 83.3% and pKpQIL transmission in K. pneumoniae by 80.8% compared to untreated controls). Plasmid transmission was reduced by concentrations of the drugs which are below peak serum concentrations and are achievable in the gastrointestinal tract. These drugs could be used to decolonize humans, animals, or the environment from AMR plasmids.IMPORTANCE More and more bacterial infections are becoming resistant to antibiotics. This has made treatment of many infections very difficult. One of the reasons this is such a large problem is that bacteria are able to share their genetic material with other bacteria, and these shared genes often include resistance to a variety of antibiotics, including some of our drugs of last resort. We are addressing this problem by using a fluorescence-based system to search for drugs that will stop bacteria from sharing resistance genes. We uncovered a new role for two drugs used to treat HIV and show that they are able to prevent the sharing of two different types of resistance genes in two unique bacterial strains. This work lays the foundation for future work to reduce the prevalence of resistant infections.

A One Health Study of the Genetic Relatedness of Klebsiella pneumoniae and Their Mobile Elements in the East of England

BACKGROUND

Klebsiella pneumoniae is a human, animal, and environmental commensal and a leading cause of nosocomial infections, which are often caused by multiresistant strains. We evaluate putative sources of K. pneumoniae that are carried by and infect hospital patients.

METHODS

We conducted a 6-month survey on 2 hematology wards at Addenbrooke's Hospital, Cambridge, United Kingdom, in 2015 to isolate K. pneumoniae from stool, blood, and the environment. We conducted cross-sectional surveys of K. pneumoniae from 29 livestock farms, 97 meat products, the hospital sewer, and 20 municipal wastewater treatment plants in the East of England between 2014 and 2015. Isolates were sequenced and their genomes compared.

RESULTS

Klebsiella pneumoniae was isolated from stool of 17/149 (11%) patients and 18/922 swabs of their environment, together with 1 bloodstream infection during the study and 4 others over a 24-month period. Each patient carried 1 or more lineages that was unique to them, but 2 broad environmental contamination events and patient-environment transmission were identified. Klebsiella pneumoniae was isolated from cattle, poultry, hospital sewage, and 12/20 wastewater treatment plants. There was low genetic relatedness between isolates from patients/their hospital environment vs isolates from elsewhere. Identical genes encoding cephalosporin resistance were carried by isolates from humans/environment and elsewhere but were carried on different plasmids.

CONCLUSION

We identified no patient-to-patient transmission and no evidence for livestock as a source of K. pneumoniae infecting humans. However, our findings reaffirm the importance of the hospital environment as a source of K. pneumoniae associated with serious human infection.

Carbapenem-Resistant Klebsiella pneumoniae: Microbiology Key Points for Clinical Practice

Carbapenemase–producing Klebsiella pneumoniae strains (Cp-Kpn) represent a challenge for clinical practitioners due to their increasing prevalence in hospital settings and antibiotic resistance. Clinical practitioners are often overwhelmed by the extensive list of publications regarding Cp-Kpn infections, treatment, characteristics, identification, and diagnosis. In this perspective article, we provide key points for clinical practitioners to consider for improved patient management including identification of risk factors and strategies for treatment. Additionally, we also discuss genetic underpinnings of antibiotic resistance, implementation of an antimicrobial stewardship program (ASP), and use of automated systems for detection of Cp-Kpn. Collectively, implementation of such key points would enhance clinical practices through providing practical knowledge to health professionals worldwide.

Assessing genetic diversity and similarity of 435 KPC-carrying plasmids

The global spread and diversification of multidrug-resistant Gram-negative (MRGN) bacteria poses major challenges to healthcare. In particular, carbapenem-resistant Klebsiella pneumoniae strains have been frequently identified in infections and hospital-wide outbreaks. The most frequently underlying resistance gene (bla_KPC) has been spreading over the last decade in the health care setting. bla_KPC seems to have rapidly diversified and has been found in various species and on different plasmid types. To review the progress and dynamics of this diversification, all currently available KPC plasmids in the NCBI database were analysed in this work. Plasmids were grouped into 257 different representative KPC plasmids, of which 79.4% could be clearly assigned to incompatibility (Inc) group or groups. In almost half of all representative plasmids, the KPC gene is located on Tn4401 variants, emphasizing the importance of this transposon type for the transmission of KPC genes to other plasmids. The transposons also seem to be responsible for the occurrence of altered or uncommon fused plasmid types probably due to incomplete transposition. Moreover, many KPC plasmids contain genes that encode proteins promoting recombinant processes and mutagenesis; in consequence accelerating the diversification of KPC genes and other colocalized resistance genes.

Increase and diversity of carbapenemase-producing Escherichia coli isolates, Italy

Aim: This study reports on a surveillance in an Italian hospital focused on carbapenemase-producing Escherichia coli (CP-Ec). Materials & methods: Eighteen isolates (nine from clinical specimens and nine from rectal swab) were characterized for antibiotic susceptibilities, typing features, main carbapenemase, extended-spectrum ß-lactamases (ESBLs) and other bla genes, and their transferability by conjugation and transformation. Results: An increase in CP-Ec isolates was observed during 3-year surveillance period. Compared with the clinical isolates, all belonging to one sequence type (ST), ST131, those from rectal swab were very heterogeneous and belonged to eight STs. Transfer data confirmed the role of conjugative plasmids in the spreading of carbapenemase genes. Conclusion: The prevalence of CP-Ec in Italy has risen, with a substantial increase over the last year.

Identification of a Carbapenemase-Producing Hypervirulent Klebsiella pneumoniae Isolate in the United States

We report on a carbapenemase-producing hypervirulent Klebsiella pneumoniae (CP-hvKP) isolate collected from a U.S. patient at an outpatient clinic. The isolate was identified as K. pneumoniae serotype K1 sequence type 23 and included both a hypervirulence (with rmpA, rmpA2 iroBCDN, peg-344, and iucABCD-iutA genes) and a carbapenemase-encoding (bla _KPC-2) plasmid. The emergence of CP-hvKP underscores the importance of clinical awareness of this pathotype and the need for continued monitoring of CP-hvKP in the United States.

Transcriptional Landscape of a bla KPC-2 Plasmid and Response to Imipenem Exposure in Escherichia coli TOP10

The diffusion of KPC-2 carbapenemase is closely related to the spread of Klebsiella pneumoniae of the clonal-group 258 and linked to IncFII_K plasmids. Little is known about the biology of multi-drug resistant plasmids and the reasons of their successful dissemination. Using E. coli TOP10 strain harboring a multi-replicon IncFII_K-IncFIB bla_KPC−2-gene carrying plasmid pBIC1a from K. pneumoniae ST-258 clinical isolate BIC-1, we aimed to identify basal gene expression and the effects of imipenem exposure using whole transcriptome approach by RNA sequencing (RNA-Seq). Independently of the antibiotic pressure, most of the plasmid-backbone genes were expressed at low levels. The most expressed pBIC1a genes were involved in antibiotic resistance (bla_KPC−2, bla_TEM and aph(3′)-I), in plasmid replication and conjugation, or associated to mobile elements. After antibiotic exposure, 34% of E. coli (pBIC1a) genome was differentially expressed. Induction of oxidative stress response was evidenced, with numerous upregulated genes of the SoxRS/OxyR oxydative stress regulons, the Fur regulon (for iron uptake machinery), and IscR regulon (for iron sulfur cluster synthesis). Nine genes carried by pBIC1a were up-regulated, including the murein DD-endopeptidase mepM and the copper resistance operon. Despite the presence of a carbapenemase, we observed a major impact on E. coli (pBIC1a) whole transcriptome after imipenem exposure, but no effect on the level of transcription of antimicrobial resistance genes. We describe adaptive responses of E. coli to imipenem-induced stress, and identified plasmid-encoded genes that could be involved in resistance to stressful environments.

A Full MALDI-Based Approach to Detect Plasmid-Encoded KPC-Producing Klebsiella pneumoniae

KPC-producing Klebsiella pneumoniae represents a severe public health concern worldwide. The rapid detection of these isolates is of fundamental importance for the adoption of proper antibiotic treatment and infection control measures, and new applications of MALDI-TOF MS technology fit this purpose. In this study, we present a full MALDI-based approach to detect plasmid-encoded KPC-producing strains, accomplished by the automated detection of a KPC-specific peak (at 11,109 m/z) by a specific algorithm integrated into the MALDI Biotyper system (Bruker Daltonik), and the confirmation of carbapenemase activity by STAR-Carba imipenem hydrolysis assay. A total of 6209 K. pneumoniae isolates from Italy and Germany were investigated for the presence of the KPC-related peak, and a subset of them (n = 243) underwent confirmation of carbapenemase activity by STAR-Carba assay. The novel approach was further applied directly to positive blood culture bottles (n = 204), using the bacterial pellet obtained with Sepsityper kit (Bruker Daltonik). The novel approach enabled a reliable and very fast detection of KPC-producing K. pneumoniae strains, from colonies as well as directly from positive blood cultures. The automated peak detection enabled the instant detection of KPC-producing K. pneumoniae during the routine identification process, with excellent specificity (100%) and a good sensitivity (85.1%). The sensitivity is likely mainly related to the prevalence of the specific plasmid harboring clones among all the KPC-producing circulating strains. STAR-Carba carbapenemase confirmation showed 100% sensitivity and specificity, both from colonies and from positive blood cultures.

Diversity among blaKPC-containing plasmids in Escherichia coli and other bacterial species isolated from the same patients

Carbapenem resistant Enterobacteriaceae are a significant public health concern, and genes encoding the Klebsiella pneumoniae carbapenemase (KPC) have contributed to the global spread of carbapenem resistance. In the current study, we used whole-genome sequencing to investigate the diversity of blaKPC-containing plasmids and antimicrobial resistance mechanisms among 26 blaKPC-containing Escherichia coli, and 13 blaKPC-containing Enterobacter asburiae, Enterobacter hormaechei, K. pneumoniae, Klebsiella variicola, Klebsiella michiganensis, and Serratia marcescens strains, which were isolated from the same patients as the blaKPC-containing E. coli. A blaKPC-containing IncN and/or IncFIIK plasmid was identified in 77% (30/39) of the E. coli and other bacterial species analyzed. Complete genome sequencing and comparative analysis of a blaKPC-containing IncN plasmid from one of the E. coli strains demonstrated that this plasmid is present in the K. pneumoniae and S. marcescens strains from this patient, and is conserved among 13 of the E. coli and other bacterial species analyzed. Interestingly, while both IncFIIK and IncN plasmids were prevalent among the strains analyzed, the IncN plasmids were more often identified in multiple bacterial species from the same patients, demonstrating a contribution of this IncN plasmid to the inter-genera dissemination of the blaKPC genes between the E. coli and other bacterial species analyzed.

Clinically Relevant Plasmid-Host Interactions Indicate that Transcriptional and Not Genomic Modifications Ameliorate Fitness Costs of Klebsiella pneumoniae Carbapenemase-Carrying Plasmids

The rapid dissemination of antimicrobial resistance (AMR) around the globe is largely due to mobile genetic elements, such as plasmids. They confer resistance to critically important drugs, including extended-spectrum beta-lactams, carbapenems, and colistin. Large, complex resistance plasmids have evolved alongside their host bacteria. However, much of the research on plasmid-host evolution has focused on small, simple laboratory plasmids in laboratory-adapted bacterial hosts. These and other studies have documented mutations in both host and plasmid genes which occur after plasmid introduction to ameliorate fitness costs of plasmid carriage. We describe here the impact of two naturally occurring variants of a large AMR plasmid (pKpQIL) on a globally successful pathogen. In our study, after pKpQIL plasmid introduction, no changes in coding domain sequences were observed in their natural host, Klebsiella pneumoniae However, significant changes in chromosomal and plasmid gene expression may have allowed the bacterium to adapt to the acquisition of the AMR plasmid. We hypothesize that this was sufficient to ameliorate the associated fitness costs of plasmid carriage, as pKpQIL plasmids were maintained without selection pressure. The dogma that removal of selection pressure (e.g., antimicrobial exposure) results in plasmid loss due to bacterial fitness costs is not true for all plasmid/host combinations. We also show that pKpQIL impacted the ability of K. pneumoniae to form a biofilm, an important aspect of virulence. This study used highly relevant models to study the interaction between AMR plasmids and pathogens and revealed striking differences from results of studies done on laboratory-adapted plasmids and strains.IMPORTANCE Antimicrobial resistance is a serious problem facing society. Many of the genes that confer resistance can be shared between bacteria through mobile genetic elements, such as plasmids. Our work shows that when two clinically relevant AMR plasmids enter their natural host bacteria, there are changes in gene expression, rather than changes to gene coding sequences. These changes in gene expression ameliorate the potential fitness costs of carriage of these AMR plasmids. In line with this, the plasmids were stable within their natural host and were not lost in the absence of selective pressure. We also show that better understanding of the impact of resistance plasmids on fundamental pathogen biology, including biofilm formation, is crucial for fighting drug-resistant infections.

Covert dissemination of carbapenemase-producing Klebsiella pneumoniae (KPC) in a successfully controlled outbreak: long- and short-read whole-genome sequencing demonstrate multiple genetic modes of transmission

BACKGROUND

Carbapenemase-producing Enterobacteriaceae (CPE), including KPC-producing Klebsiella pneumoniae (KPC-Kpn), are an increasing threat to patient safety.

OBJECTIVES

To use WGS to investigate the extent and complexity of carbapenemase gene dissemination in a controlled KPC outbreak.

MATERIALS AND METHODS

Enterobacteriaceae with reduced ertapenem susceptibility recovered from rectal screening swabs/clinical samples, during a 3 month KPC outbreak (2013-14), were investigated for carbapenemase production, antimicrobial susceptibility, variable-number-tandem-repeat profile and WGS [short-read (Illumina), long-read (MinION)]. Short-read sequences were used for MLST and plasmid/Tn4401 fingerprinting, and long-read sequence assemblies for plasmid identification. Phylogenetic analysis used IQTree followed by ClonalFrameML, and outbreak transmission dynamics were inferred using SCOTTI.

RESULTS

Twenty patients harboured KPC-positive isolates (6 infected, 14 colonized), and 23 distinct KPC-producing Enterobacteriaceae were identified. Four distinct KPC plasmids were characterized but of 20 KPC-Kpn (from six STs), 17 isolates shared a single pKpQIL-D2 KPC plasmid. All isolates had an identical transposon (Tn4401a), except one KPC-Kpn (ST661) with a single nucleotide variant. A sporadic case of KPC-Kpn (ST491) with Tn4401a-carrying pKpQIL-D2 plasmid was identified 10 months before the outbreak. This plasmid was later seen in two other species and other KPC-Kpn (ST14,ST661) including clonal spread of KPC-Kpn (ST661) from a symptomatic case to nine ward contacts.

CONCLUSIONS

WGS of outbreak KPC isolates demonstrated blaKPC dissemination via horizontal transposition (Tn4401a), plasmid spread (pKpQIL-D2) and clonal spread (K. pneumoniae ST661). Despite rapid outbreak control, considerable dissemination of blaKPC still occurred among K. pneumoniae and other Enterobacteriaceae, emphasizing its high transmission potential and the need for enhanced control efforts.